Movahednejad - PHD Student Mechanical Engineering
Ommi - Assistant Professor, Tarbiat Modarres University
Hosseinalipour - Assistant rofessor, Science and Technology University of Iran

For spark ignition engines, the fuel-air mixture preparation process is known to have a significant influence on engine performance and exhaust emissions. In this paper, an experimental study is made to characterize the spray characteristics of an injector with multi-disc nozzle used in the engine. The distributions of the droplet size and velocity and volume flux were characterized by a PDA system. Also a model of a 4 cylinder multi-point fuel injection engine was prepared using a fluid dynamic code. By this code one-dimensional, unsteady, multiphase flow in the intake port has been modeled to study the mixture formation process in the intake port. Also, One dimensional air flow and wall fuel film flow and a two dimensional fuel droplet flow have been modeled and it includes the effects of in-cylinder mixture back flows into the port. Accuracy of model was verified using experimental results of engine testing and it shows good agreement between the model and the real engine. As a result, predictions are obtained that provide detailed picture of the air-fuel mixture properties along the intake port. A comparison was made on engine performance and exhaust emission in different fuel injection timing for 2600 rpm and different loads. According to the present investigation, a key point was found to design optimum injection timing for different engine operating conditions.

MPFI Engine, Injection Timing, Performance, Emission